1. Field of the Invention
The present invention relates in general to polymer vapor surface treatments and coatings, in particular to polymer vapor surface treatments and coatings as applied to musical instrument strings; even more specifically, it relates to polytetrafluoroethylene (“PTFE”) polymer vapor surface treatments and coatings applied to musical instrument strings.
2. Background Information
The invention described and claimed herein comprises a vapor phase polymeric surface treatment. One specific application of such a surface treatment is applied to musical instrument strings. Examples of such strings are guitar, violin, cello, bass, piano and harp strings.
Surface coatings, and surface treatments, are well-known in the art. As used herein, surface coating means an attached laminate or jacket, positioned on the substrate, while surface treatment means a modified surface region of the substrate which is in fact part of the substrate.
A musical instrument string typically comprises a core of material and optionally additional strands of the same or other material wound around the core. The composition and dimensions of the core and the optional windings are chosen so as to produce the desired tones when the string is caused to vibrate.
U.S. Pat. No. 4,945,856 deals with the vapor deposition of parylene polymer in low vacuum. This material has been used in the electronics and medical area, but it has several times higher friction coefficient as does PTFE. The process is performed in a lesser degree of vacuum, which does not offer the same purity as high vacuum processes. The level of adhesion of this coating does not lend itself to applications where surface abrasion (strumming) is an issue as it can fray and delaminate fairly easily from the coated article. There exist stronger binding forces within the coating itself than between the coating and substrate. It is believed that this effect is responsible for the way in which a parylene coating can be peeled from the substrate, whereas the PTFE polymer vapor surface treatment can not.
U.S. Pat. No. 3,767,559 deals with RF sputter deposition of PTFE as an improvement over DC means, which are not applicable to insulators such as PTFE, but does not mention the use as a coating on musical strings.
U.S. Pat. No. 4,539,228 deals with extending the life of musical instrument strings through the application of PTFE in an oil lubricant. While some of the benefits of applying PTFE to a musical string are gained, the material is not adhered to the surface in the same way that a vapor deposited polymer is condensed and nucleated onto the surface.
U.S. Pat. No. 5,578,775 discloses a musical instrument string having an inner bundle embedded in a mantle of precious metal and an abrasive resistant treatment of short regions of the string (those which are either struck while playing or which contact the instrument) and discloses surface hardening using phosphate coating, vapor plating, flame coating or ion plating.
U.S. Pat. No. 5,883,319 deals with the bonding of a GORETEX(™) expanded PTFE (“e-PTFE”) gauze to the surface of the wound type of musical instrument strings, using an adhesive. The gauze sheet is then covered with a heat shrink or polymer jacket.
U.S. Pat. No. 5,888,591 teaches deposition of PTFE using Chemical Vapor Deposition (CVD), with no specific mention of use for musical strings. The preferred method in the current invention uses Physical Vapor Deposition (PVD) which has been documented to result in a harder, more wear resistant polymeric-material, possibly attributed to the higher degree of cross linking of the polymeric material resulting from PVD processing.
A general reference describing deposition techniques and alternatives is “Plasma Deposition and Treatment of Polymers”, ed. W. W. Lee, R. d'Agostino, and M. R. Wertheimer, ISBN 1-55899-450-5, published by Materials Research Society.
Spray type coatings have been applied to musical instrument strings, but can affect the musical quality as they change the mechanical properties of the string due to excessive coating thickness, and the attached laminate being distinct from the substrate, causing deadening of the musical sound. The “Black Maxima” TEFLON (™) spray coated string had been previously marketed by Maxima, approximately 10 years ago. Applicants believe that this product was discontinued as the coating would become unattached from the string, and degrade musical performance. Also, the high temperature oven baking processes used to cure spray type coatings onto the surface can harm the base metal. Oil based and other wipe-on type coatings are not well adhered to the substrate, and will offer only short term benefits. Still other types of extruded coatings or jacketed coatings can adversely affect sound quality, due to the damping of the sound vibrations and subsequent muffling of the sound.